Adjustable depth of field optical coherence tomography

A method of surface inspection of an object using optical coherence tomography (OCT), the method comprising:

• determining a first working distance between a scanner head and a first surface location on the object;
• determining a first depth of field, based on the first working distance, in which the surface of the object at the first surface location is in focus;
• changing a current depth of field to the first depth of field;
• performing an A-scan of the object;
• moving the object relative to the scanner head;
• determining a subsequent working distance being a distance between the scanner head and a subsequent surface location of the moved object;
• determining whether the object is in focus at the subsequent surface location, if the object is not in focus:
• determining a subsequent depth of field, based on the subsequent working distance, in which the surface of the object at the subsequent surface location is in focus;
• changing the current depth of field to the subsequent depth of field;
• and
• performing an A-scan of the object;
• and
• otherwise, performing an A-scan of the object.